The present invention relates to a radio paging system and, more particularly, to a paging system which offers a service at several different bit rates and a receiver for the same.
Current trend in the paging systems is toward a higher bit rate, which would accommodate the increase in traffic as well as improve the effective use of the available frequency allocations. A method heretofore proposed for increasing the bit rate of a paging signal consists in simply multiplying the clock frequency by N to make the bit rate N-fold. This kind of method, however, has the following problems.
(1) Receivers of different bit rates cannot coexist in a single paging system; and
(2) While each codeword usually undergoes error correcting coding, an increase in bit rate results in a decrease in the time length of one codeword and, therefore, the signal becomes susceptible to burst errors which frequently occur on radio channels due to fading.
Another prior art implementation for providing higher bit rates is changing the bit rate depending upon the kind of information (e.g. 300 bits per second for an address and 600 bits per second for a message), as disclosed in, for example, U.S. Pat. No. 4,642,632 which is assigned to the applicant of the instant application and issued Feb. 10, 1987 to Ohyagi et al. Such an implementation, however, is incapable of changing the bit rate depending upon the particular traffic or messages to be transmitted because the bit rate for any one kind of information is fixed (e.g. 300 bits per second for an address without exception).